Last month I got obsessed with the CD4023 Pulse Width Oscillator that Rykhaard / Richarius had posted over on The Sound of Logic / Deathlehem forum. I found messages here mentioning it, but I could not find the schematic itself here.

So I built it and really loved it. Then, instead of working on my long-overdue suitcase synth, I became obsessed with automatizing several things with this circuit (which is now destined for said suitcase synth!)...

Then I added the CV part to it, as devised by Rykhaard. Despite not being able to get the full range, it was still a lot of fun. I'd take the output of a 4-bit random generator into an R/2R and use that as a CV. Fun.

Then, wanting to replace the rotary switch that selects the capacitor in the circuit, I used a 4051 with 3 switches to choose 1 of 8 caps. But then of course, when one has an electronic switch, one can make that automatic. So 3 oscillators feed that, switching the cap. Crazy. Fun.

Then I eyed the feedback pot in the circuit. To replace it, I generate a voltage using a 4-bit random gen into an 2/2R. The resulting voltage feeds an LED in a home-rolled opto-isolator (AKA Vactrol), and the resulting resistance from the LDR is used instead of the pot. Crazy. Fun.

With all these things going at once, the sounds are pretty crazy. I tried adding slew/portamento/glide to one of the random CV's, but with all the cap-switching, it wasn't noticeable.

Almost all my breadboards are used, and they are sprawling all over the place.

And I want to further the self-playing ever-changing automaticness of this beast. I have some ideas, but I need a triangular VLFO, very slow, like 1 cycle per hour or maybe even 1 cycle per 17 minutes or something. I've had no luck with the old 4069 or LM324 LFO circuits. I have been racking my brain trying to figure out how to get a 4029 to count up then down all by itself. Anyway, that's possibly another thread.

This is a video of the earlier incarnation, with the CV input driven by a 4bit random generator into an R/2R : http://www.youtube.com/watch?v=JWXbtgKunJY . There's also a 4046 VCO following the same random voltage.

I've also had alot of fun with this circuit! I made mine out of a 4093 and some mml. (I see you've seen)
As far as drawing a line, if you're really asking, who needs a line?
It looks like you cold develop quite a few different modules based on the same circuit.
Just keep notes!

In answer to your first question:
One does not stop, one gets more shelves and more space and more parts and continues building the robots.

Carry on the good work and get something soldered up so you have some breadboard space again remember to do a circuit diagram first._________________As a mad scientist I am ruled by the dictum of science: "I could be wrong about this but lets find out"

Any chance you can share that circuit from Deathlehem?
I have had nothing but bad luck with that site [...]

I admit I had some trouble there too... it took weeks before my messages were put up, since they required approval first. But I think it's a probation period, wherein you have to post 3,4 times and then you can post freely. I think also the guy who runs it, who is in fact the same who drew up this schematic, was down and decided to close the site for good (a decision now reversed), so perhaps you got him at that wrong time and he didn't bother approving you because what's the use if the board was shutting down? Perhaps try again, and use the same alias as here...

I find that no matter how many breadboards I have, I still manage to end up with them full of circuits. There must be some kind of law here - you can never have enough breadboard space. At the moment I have the randomizer, an experimental lunetta mixer, a slow-clocked white noise generator test circuit and a multi-synth mixer prototype all on the go. The answer is to commit them to PCB (or perfboard). The trouble is, I'm only 100% happy with the randomizer (I think). I think I'll do something about that tomorrow (although I always say that). Now, of course, I'd like to try out this 4023 circuit as well as hundreds more circuits that I've seen. I think that this website can only lead to madness (although I'm already there ).

Committing to PCB/perfboard is tough for me. I want to make absolutely sure that I am 100% happy with the circuit, that the cap values and pot ranges are the most useful, etc. When I build a box, I usually still have the actual circuit still on the breadboards in case. And despite my careful planning, I still sometimes make changes to the box afterwards.

As for having a pile of circuits to try, well, yeah, this site certainly has a wealth of great ideas. It can be overwhelming as one's list gets longer and longer. I figure it's better to have lots of ideas than no ideas.

I also keep a breadboarded version on standby until I'm 100% happy with the hard-wired version. This is because, although I have a circuit diagram, I sometimes make small changes and forget to update the drawing/printout. Secondly, you can compare the performance of the 'properly' built one against the breadboard example (I have found the odd mistake at this stage). I once had a sample and hold circuit which worked perfectly well on the breadboard, but leaked alarmingly on PCB. It turned out that it was due to two tracks running close and parallel to each other. When I amended this, it worked. I think that it was down to the two tracks acting as a capacitor (but I'm still not totally sure).

As for the number of ideas, I'm glad that there are so many here. It's which one to try next that's my problem...

One year later, and a couple of time-consuming massive projects done, I finally figured out all the circuits and putting this thing in a box. With what I hope is a good mix of playability and standalone options.

Some of the soldering is done, but at the moment, I'm stalled due to trying to work out technical details involving the enclosure... there's a special thing I'm trying to do, which I think is going to be quite cool if I can pull it off. It's secret right now .

I'm interested in how that oscillator acctually works or acheives PWM, I just breadboarded the above circuit diagram with a different kind of IC (2 input NOR) thinking this would work because it's basically the dual inverter oscillator with some extras, but it didn't work.
I honestly didn't expect it to but the note on the circuit diagram got my hopes up. It half worked, I ghot a bit of frequency deviation but hardly any and it only changed one half of the duty cycle, as I expected it might from the way transistors work.
Must it be a 4023? if so, why? has anyone acctually got it working exactly like it is in the diagram?_________________As a mad scientist I am ruled by the dictum of science: "I could be wrong about this but lets find out"

Alas, I've forgotten any discussion or explanations from the original thread on Deathlehem, which are now lost forever. There was mention that one could use a different chip than the 4023 (possibly only 2 inputs are needed, and if faulty memory serves, someone built it with a 4093?).

As for whether it really does PWM, I don't know... I never actually checked or cared... I just liked what I was hearing, and just assumed that Ryk had named it accurately.

I'm interested in how that oscillator acctually works or acheives PWM, I just breadboarded the above circuit diagram with a different kind of IC (2 input NOR) thinking this would work because it's basically the dual inverter oscillator with some extras, but it didn't work.

It will work with NORs. You just need to change the 100k pull-up to pull-down and reverse the diode if you want gating capability.

I thought so, however I noted almost no effect fron the voltage control transistor: it changed the time of one half of the duty cycle then cut out after some really dodgy high frequency oscillation at one specific control voltage.

I'm really interested to get the effect that the original poster acheived, this could be a fantastic VCO but I'm thinking perhaps the diagram is wrong? I'll have to do some more tests, does anyone have any ideas?_________________As a mad scientist I am ruled by the dictum of science: "I could be wrong about this but lets find out"

Basically, each of the 4 basic parameters of the circuit has several options... they can be adjusted manually or automatically (the latter via LFO or external CV). The idea is that the box can be played performatively, or used as a standalone installation.

For each section, a couple of switches, a pot and a 4053 allow one to use the pot manually directly, or as the speed control for the LFO.

Feedback level is controlled by a hand-rolled "vactrol" LED-LDR.

The range section is a bit more complicated: 8 different capacitors can be selected manually via the 3-bit switches (thus interfacing a 4051), or pseudo-randomly. The latter uses a 4006 & 4070 3-bit generator, whose clock rate can be controlled manually or automatically.

LFOs are triangular, based on a simple 40106 circuit. The end result of everything is made triangular via a 4015 wave-shaper.

The cool feature of the box is of course is the infinity mirror. The LEDs therein echo the state or value of the various sections, e.g. oscillator rate, feedback level and range choice (3 bit), 2 LEDs each. The meters show the internal voltage level ultimately controlling the speed of the oscillators.

For Burroughs and the "23 enigma" watchers... the main circuit uses a CMOS 4023 chip, the range on the meters go from 2 to 23 (in prime numbers, and VdGG units (because I was heavy into Peter Hammill & Van der Graaf Generator during part of the design phase)).

Thanks to Ryk for the original 4023 circuit, JingleJoe for invaluable assistance and circuits, PHOBoS for inspiration, and all y'all here in the electro-music forums for circuits, inspiration and moral support.

For Burroughs and the "23 enigma" watchers... the main circuit uses a CMOS 4023 chip, the range on the meters go from 2 to 23 (in prime numbers, and VdGG units (because I was heavy into Peter Hammill & Van der Graaf Generator during part of the design phase)).

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